What is the phase angle between the voltage across and the current through a series RLC circuit if XC is 25 ohms, R is 100 ohms, and XL is 75 ohms?
Why In a series RLC circuit the reactances subtract: X = XL - XC = 75 - 25 = 50 ohms, and the net result is inductive since XL is larger. The phase angle is arctan(X/R) = arctan(50/100) = arctan(0.5), about 27 degrees. Because the net reactance is inductive, the voltage leads the current (ELI: E leads I in an inductor).
Watch out The 63 degree choices come from flipping the ratio and taking arctan(R/X) = arctan(100/50); the tangent of the phase angle is always reactance over resistance. The lagging choices would apply only if the net reactance were capacitive, meaning XC larger than XL.
ELI the ICE man: net XL wins, voltage leads. Angle = arctan(X/R), reactance on top.